Building Control & external concrete blocks (waterproofing).

[SpecialK]

Hi,
I have an extension built from 7N concrete blocks on the outside. BC have been around for final sign off but they want the blocks rendered or clad (final waterproofing?).
I would like to know if this is correct and it actually needs doing for sign off - I have seen various industrial buildings left as just blocks? I will be cladding the blocks eventually so it doesn't really matter either way, just be nice to get the sign off sooner...

I also need to do the two sides of the extension that are hard to get to. Does anyone know of a waterproofing paint that can go straight on the concrete blocks that would satisfy BC?

 

[^woody^]

Most blocks are OK on their own if pointed, but block wall u-values are typically based on the external being rendered.

 

[SpecialK]

They have not mentioned U Values - only having waterproofing! I will have a look to see if I can find some form of supporting evidence to say they are OK left as they are. All joints are pointed..

Good point about the insulation values, always good to get more warmth!

Most blocks are OK on their own if pointed, but block wall u-values are typically based on the external being rendered.

 

[freddiemercurystwin]

It's a traditional cavity wall presumably?

 

[SpecialK]

Yes, 100mm full fill dritherm 32 with thermalites on the inside.

It's a traditional cavity wall presumably?

 

[freddiemercurystwin]

Then ask him why you don't need to add a finish to a brick external skin.

 

[designinsteel]

Building control will probably defer to the NHBC guidance if you show them the following:

Freeze/thaw and sulfate attack
Concrete blocks used in the outer leaf without protective cladding or render should:

• have a compressive strength >7.3N/mm2 or have a density of at least 1,500kg/m3
• be made with dense aggregate to BS EN 12620, or
• be aircrete concrete blocks having had their suitability confirmed by the manufacturer.

 

[freddiemercurystwin]

.

 

[SpecialK]

Brilliant, this gives me something to go back to them with! They are 7N's so the first is OK.
I cant see anything about the aggregate mix but under water absorption it says "NPD EN 771-3 : 2013" - Any idea what that means?

https://dam-assets.apps.travisperkins.group/lxRD9/GPID_1000194641_DOP_00.pdf

Building control will probably defer to the NHBC guidance if you show them the following:

Freeze/thaw and sulfate attack
Concrete blocks used in the outer leaf without protective cladding or render should:

• have a compressive strength >7.3N/mm2 or have a density of at least 1,500kg/m3
• be made with dense aggregate to BS EN 12620, or
• be aircrete concrete blocks having had their suitability confirmed by the manufacturer.

 

[designinsteel]

The EN number is the Eurocode spec that this feature is tested against. "NPD" means "No product data", so I believe it means it hasn't been certified for this.

 

[John D v2.0]

The EN number is the Eurocode spec that this feature is tested against. "NPD" means "No product data", so I believe it means it hasn't been certified for this.

Just an inconsequential correction is that it's "No Performance Determined" but basically the same thing